Canon's PowerShot series is their point-and-shoot series, so it lacks a lot of the capabilities offered by DSLRs. CHDK (Canon Hacking Development Kit) allows me to set the aperture, bracketing and other settings I normally can't. Here's a link if you're interested in reading more: http://chdk.wikia.com/wiki/CHDK
The big advantage to using CHDK is that I can control the exposure, over-riding the camera's automatic detection. In addition, CHDK allows me to shoot in RAW instead of JPEG.